This invention relates to rotor blades, and in particular to a load absorbing member or members incorporated in the design of the rotor blades which assist in reducing both flapwise and chordwise bending moments, torsional loading and reduce or eliminate the control system loads induced by rotor blade moment stall.
In a general sense, the designer of helicopter rotor blades always strives to maintain the loading on the rotor blades within acceptable limits, while at the same time avoiding unnecessarily burdening a design with added weight. The trend has been toward the "new" materials including the nonmetallic materials such as fiberglass. The loading on a given rotor blade design, however, is not necessarily reduced by the use of a different material. Instead, the rotor blade may be better able to withstand the loading, or it may redistribute the loading. To reduce the loading is a problem unique in itself and one that is not always readily solvable.
Consider for example the aerodynamic phenomenon associated with helicopter rotor blades known as rotor blade moment stall. Generally this phenomenon is understood to occur at a critical blade angle of attack, where there is an aft movement of the aerodynamic center and it has a nonlinear motion with oscillatory angle of attack changes. As the forward speed of the helicopter increases, the angle of attack of the retreating blade increases in a cyclic fashion until the critical angle of attack is reached with the noted moment stall regime. One of the effects produced by this moment stall, and one which grows in severity as the rotor blade penetrates the moment stall regime, is a rapid growth in control system loads. This rapid growth of the control system loads severely limits the forward speed capability of the aircraft.
It would therefore be desirable to develop means for eliminating or at least decreasing the control system load growth, rather than increasing the size of the control system components or limiting the forward flight speed. Quite obviously increasing the size of the control system is undesirable because of the resulting weight penalty and associated problems. It would be most desirable, accordingly, to develop means for eliminating or at least decreasing the control system load growth while retaining present control system designs.